Bacterial mutants "gro" for phages S13, sigma x 174 and G4 are to be isolated in a search for gene products essential to phage DNA replication. The map position and function of such genes will be determined. Bacterial mutants "gro-" for phage M13 will be isolated in a search for mutations in the sigma subunit of E. coli RNA polymerase. Treatments causing altered in vivo regulation of protein synthesis of small DNA phages will be analyzed to determine the cause of the alterations.